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Commit 5fdf5d37 authored by Boris Ostrovsky's avatar Boris Ostrovsky Committed by Ingo Molnar
Browse files

x86/xen: Avoid fast syscall path for Xen PV guests 



After 32-bit syscall rewrite, and specifically after commit:

  5f310f73 ("x86/entry/32: Re-implement SYSENTER using the new C path")

... the stack frame that is passed to xen_sysexit is no longer a
"standard" one (i.e. it's not pt_regs).

Since we end up calling xen_iret from xen_sysexit we don't need
to fix up the stack and instead follow entry_SYSENTER_32's IRET
path directly to xen_iret.

We can do the same thing for compat mode even though stack does
not need to be fixed. This will allow us to drop usergs_sysret32
paravirt op (in the subsequent patch)

Suggested-by: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: david.vrabel@citrix.com
Cc: konrad.wilk@oracle.com
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1447970147-1733-2-git-send-email-boris.ostrovsky@oracle.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1ec21837

arch/x86/entry/entry_32.S

+3 −2
Original line number Diff line number Diff line
@@ -308,8 +308,9 @@ sysenter_past_esp: 


	movl	%esp, %eax

	call	do_fast_syscall_32

	testl	%eax, %eax

	jz	.Lsyscall_32_done

	/* XEN PV guests always use IRET path */

	ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \

		    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV



/* Opportunistic SYSEXIT */

	TRACE_IRQS_ON			/* User mode traces as IRQs on. */

arch/x86/entry/entry_64_compat.S

+6 −4
Original line number Diff line number Diff line
@@ -121,8 +121,9 @@ sysenter_flags_fixed: 


	movq	%rsp, %rdi

	call	do_fast_syscall_32

	testl	%eax, %eax

	jz	.Lsyscall_32_done

	/* XEN PV guests always use IRET path */

	ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \

		    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV

	jmp	sysret32_from_system_call



sysenter_fix_flags:
@@ -200,8 +201,9 @@ ENTRY(entry_SYSCALL_compat) 


	movq	%rsp, %rdi

	call	do_fast_syscall_32

	testl	%eax, %eax

	jz	.Lsyscall_32_done

	/* XEN PV guests always use IRET path */

	ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \

		    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV



	/* Opportunistic SYSRET */

sysret32_from_system_call:

arch/x86/include/asm/cpufeature.h

+1 −0
Original line number Diff line number Diff line
@@ -216,6 +216,7 @@ 
#define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */

#define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */

#define X86_FEATURE_VMMCALL     ( 8*32+15) /* Prefer vmmcall to vmcall */

#define X86_FEATURE_XENPV       ( 8*32+16) /* "" Xen paravirtual guest */





/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */

arch/x86/xen/enlighten.c

+3 −1
Original line number Diff line number Diff line
@@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic); 


static void xen_set_cpu_features(struct cpuinfo_x86 *c)

{

	if (xen_pv_domain())

	if (xen_pv_domain()) {

		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);

		set_cpu_cap(c, X86_FEATURE_XENPV);

	}

}



const struct hypervisor_x86 x86_hyper_xen = {